This project addresses a key question about the role of CD8+ cytotoxic T lymphocytes (CTLs) in HIV-1 pathogenesis, which is how the differentiation state of HIV-1-infected CD4+ T lymphocytes affects susceptibility to killing by CTLs. Given that CD4+ T lymphocytes also contain cytolytic machinery, it is likely that they have similar mechanisms to CTLs to protect themselves from cytolysis, which may help render them resistant. The expression of cytolytic proteases is highly dependent on cell differentiation/activation, as is HIV-1 protein expression. It is therefore unclear how these opposing factors balance each other. Our aims to explore these issues are: 1. To assess the susceptibility of epitope-loaded or HIV-1-infected CD4+ T lymphocytes in different stages of differentiation/activation to killing by CTLs; 2. To evaluate how Nef affects the susceptibility of CD4+ T lymphocytes in different stages of differentiation to the antiviral effects of CTLs; 3. To explore strategies to enhance CTL killing of HIV-1-infected CD4+ T lymphocytes that are relatively resistant to killing. These concepts are highly relevant to understanding how HIV-1 persists in the face of a generally potent CTL response, especially how infected cells can survive to revert from activated effectors to resting memory cells bearing the latent reservoir, and how well CTLs would kill infected cells that are stimulated to purge this reservoir in shock and kill strategies being considered for cure of HIV-1 infection.